The present invention relates, in general terms, to torsion-damping devices of the kind conventionally used in a clutch plate assembly, especially for a motor vehicle, to minimise the vibrations which are liable to arise along the kinematic chain in which the assembly is located, and thereby to ensure a controlled transmission of the torque applied to the clutch.
The present invention is aimed, more particularly, at torsion-damping devices of this kind which comprise two separate damping stages, namely a first stage of relatively lower rigidity and a second stage of relatively greater rigidity, which are arranged axially next to one another on a common hub and each of which have two coaxial parts mounted to rotate relative to one another against the action of elastic members interposed circumferentially between them.
Such a torsion-damping device is described, for example in French Pat. Nos. 1,501,465 and 2,376,333.
In French Pat. No. 2,376,333 the first damping stage comprises, transversely, two annular flanges located substantially in the same plane one around the other, the elastic members interposed circumferentially between these two flanges bearing, at one end on one of these flanges and at the other end on the other flange.
The advantage of this arrangement is that it results in a minimum axial bulk.
However, it has several disadvantages.
First of all, the two flanges used are not identical and therefore each need to be manufactured separately.
Furthermore, being spaced out radially, they result overall in a considerable radial bulk which can rule out certain applications.
Moreover, since the elastic members interposed circumferentially between these flanges bear at each of their ends on a single element only, which consists of one or other of these flanges, the stability, parallel to the axis of the assembly, of these elastic members is not properly controlled, and during operation these elastic members may move laterally, parallel to the axis of the assembly, to the detriment of their working condition.
Finally, the specific arrangement one around the other of the two flanges necessarily implies a paired association of elastic members, the two elastic members of one and the same pair being mounted in opposition to one another, one being compressed when the other expands, and vice versa, so that the torque resulting overall from the assembly of these elastic members is, for a given bulk, necessarily less than that switch is normally possible by means of elastic members all acting in the same direction.
In practice, these elastic members are necessarily very flexible, and they are therefore particularly sensitive during operation, to the effects of centrifugal forces, again to the detriment of their stability.
In French Pat. No. 1,501,465, one of the coaxial parts of the first damping stage comprises, transversely, a flange rotating integrally with the hub of the assembly, whilst the other comprises transversely, on either side of said hub flange, two elements referred to as guide elements, which are integral with one aonther and with one of the coaxial parts of the second damping stage, the other of the coaxial parts of the second damping stage engaging said hub flange with play.
In practice, in this French Pat. No. 1,501,465, the two guide elements used in this way, which are provided to ensure improved location during operation of the corresponding elastic members, both consist of two annular washers which extend circularly in a continuous manner around the hub of the assembly.
The result of this is a considerable outlay of metal and, axially, a large overall bulk of the assembly.
This is all the more so because, by virtue of the construction, the elastic members of the first damping stage are arranged either on a circumference of the assembly having a diameter substantially equal to that on which the elastic members of the second damping stage are located elsewhere, or on a circumference having a diameter less than that of the latter circumference, in this case, in line with the fixing means used elsewhere to effect the assembly of the various parts constituting one of the coaxial parts of this second damping stage.
Finally, in this French Pat. No. 1,501,465, the guide washers of the first damping stage each have, in known manner, in a position corresponding to each of the elastic members in question, an aperture in which an elastic member is partially axially engaged, in such a way that, although these guide washers assist in locating these elastic members, this location is not completely guaranteed.
The object of the present invention is, in general terms, to provide an arrangement which makes it possible to avoid the disadvantages briefly described above and which also leads to other advantages.